Subtemporal Approach and Its Infratentorial Extension: Review and a Comparative Analysis of Different Techniques

Introduction Surgical resection of lesions occupying the incisural space is challenging. In a comparative fashion, we aimed to describe the anatomy and surgical approaches to the tentorial incisura and to the rostral brainstem via the intradural subtemporal approach and its infratentorial extensions. Methods Six fresh human head specimens (12 sides) were prepared for the microscopic dissection of the tentorial incisura using the intradural subtemporal approach and its infratentorial extensions. Endoscope was used to examine the anatomy of the region inadequately exposed with the microscope. Image-guided navigation was used to confirm bony structures visualized around the petrous apex. Results Standard subtemporal approach provides surgical access to the supratentorial brainstem above the pontomesencephalic sulcus and to the lateral surface of the cerebral peduncle. The linear or triangular tentorial divisions can provide access to the infratentorial space below the pontomesencephalic sulcus. The triangular tentorial flap in comparison with the linear incision obstructs the exposure of anterior incisural space and of the prepontine cistern. Visualization of the brainstem below the trigeminal nerve can be achieved by the anterior petrosectomy. Conclusion Infratentorial extension of the intradural subtemporal approach is technically demanding due to critical neurovascular structures and a relatively narrow corridor. In-depth anatomical knowledge is essential for the selection of the appropriate operative approach and safe surgical resections of lesions.

Microsurgical Resection of a Petroclival Epidermoid Cyst Using an Anterior Petrosectomy Approach: 2-Dimensional Operative Video

Epidermoid cysts are rare, benign lesions that result from inclusion of ectodermal elements during neural tube closure.1 Cysts are composed of desquamated epithelial cells and restrict diffusion on magnetic resonance imaging (MRI).2,3 Symptoms are attributable to anatomic location.4,5 In this video, we illustrate the surgical treatment of an epidermoid cyst located in the right cerebellopontine angle, petrous apex, and Meckel's cave. The patient, a 33-yr-old female with right-sided V1 trigeminal hypoesthesia, underwent surveillance imaging for 2 yr. However, she developed progressive V1 and V2 trigeminal hypoesthesia and imaging revealed enlargement of the lesion. Therefore, surgical resection was pursued. The patient consented to the procedure. The patient underwent a right middle fossa craniotomy and anterior petrosectomy. After identifying the greater superficial petrosal nerve and cutting the middle meningeal artery as it exited foramen spinosum, Kawase's triangle was drilled, and the dura over Meckel's cave and the subtemporal dura were opened. The lesion was resected, taking care to preserve the trigeminal nerve and the basilar artery. A retrosigmoid craniotomy was then fashioned. The cyst and its capsule were dissected off the brainstem and cranial nerves utilizing natural corridors between the trigeminal and vestibulocochlear nerves as well as between the facial and lower cranial nerves. Gross total resection was confirmed on postoperative MRI, and she was discharged home on postoperative day 5. Three months after surgery, she underwent formal pinprick testing, which revealed 95% loss of sensation in V1, 20% loss in V2, and normal sensation in V3. Three-month postoperative MRI showed no residual tumor.

Treatment and Outcome of Anterior Inferior Cerebellar Artery (AICA) Aneurysms: Helsinki Series of 15 Consecutive Patients.

Background: Anterior inferior cerebellar artery (AICA) aneurysms are rare posterior circulation lesions that are challenging to treat.Objectives: To present the treatment and clinical outcome of AICA aneurysms in an unselected cohort of patients.Methods: A retrospective analysis of patient record files, DSA and CT angiography images of 15 consecutive patients harboring AICA aneurysms treated between 1968 to 2017. Results: Eighty percent of the AICA aneurysm patients were females. Twenty percent presented with intracerebral hemorrhage (ICH) and 40% had intraventricular hemorrhage. Eleven (73%) patients suffered from subarachnoid hemorrhage (SAH); a good-grade SAH (Hunt and Hess grade 1-3) was observed in 82 % SAH patients. Surgery was performed in 73 % patients. Coil embolization was done in 7% patients and 20 % patients were treated conservatively. In 73 % patients retrosigmoid approach was used and in 27 % patients a sub-temporal approach with anterior petrosectomy was applied. A parent vessel occlusion was needed to occlude the aneurysm in 18 % patients.Conclusion: Surgical treatment of AICA aneurysms has a high rate of cranial nerve deficits but most of patients have a good long-term clinical outcome. Surgical treatment may be an option only in selected cases of AICA aneurysms.

Use of Neuroanatomic Knowledge and Neuronavigation System for a Safe Anterior Petrosectomy

Introduction: The petroclival region is among the most challenging anatomical areas to deal with in skull base surgery. Drilling of the anterior part of the petrous bone during the anterior transpetrosal approach involves the risk of injury of the cochlea, superior semicircular canal, internal carotid artery, and internal auditory canal. A thorough understanding of the microneurosurgical anatomy of this region is mandatory to execute the transpetrosal approaches, decreasing the risk of complications. The aim of this study is to describe the anatomical structures of the petroclival region, highlighting the importance of neuronavigation for safe performance of the anterior transpetrosal approach. Methods: Three adult cadaveric human heads were formalin-fixed and injected with colored silicone. They underwent an axial 1 mm slab CT scan, which was used for neuronavigation during the surgical approaches. The anterior petrosectomy was performed with the aid of neuronavigation during the drilling of the petrous bone. The surgical management of a patient harboring a petroclival meningioma, operated on using an anterior transpetrosal approach, was reported as an illustrative case. Results: The anterior petrosectomy was completed accurately with wide exposure of the surgical target without injuring the cochlea and other structures in all three cadaveric specimens. In the surgical case, no approach-related complications occurred, and a gross total resection of the tumor was achieved. Conclusions: Deep knowledge of the location and relationships of the vital elements located within the temporal bone, along with the use of neuronavigation, are the key aspects to perform the anterior transpetrosal approach safely, reducing the risk of complications.

Anatomical Step-by-Step Dissection of Complex Skull Base Approaches for Trainees: Surgical Anatomy of the Middle Fossa Approaches and Anterior Petrosectomy, Surgical Principles, and Illustrative Cases

Introduction The middle fossa (MF) approaches encompass a group of versatile surgical accesses to pathologies in the MF, internal auditory canal (IAC), and superomedial aspect of the posterior fossa. Although many descriptions of the MF approaches have been published, a practical surgical guide that allows an easy understanding for Skull Base trainees is needed. Methods Three formalin-fixed, colored-injected specimens were dissected under microscopic magnification (six sides). A MF craniotomy followed by IAC drilling was performed on three sides, and anterior petrosectomy (AP) was performed in the remaining three sides. The anatomical dissection was documented in stepwise three-dimensional photographic images. Following dissection, representative case applications were reviewed. Results The MF approach provides direct access to the MF structures and IAC. The AP provides excellent access to the superomedial aspect of the posterior fossa. Key common steps include: positioning and skin incision; scalp and muscle flaps; burr holes; craniotomy flap elevation; dural dissection along the petrous ridge; division of the middle meningeal artery; and exposure of the greater superficial petrosal nerve, tegmen tympani, and V3. Then, to approach the IAC: superior IAC drilling, and longitudinal dura opening. The area drilled in the AP approach forms a pentagon limited by the petrous internal carotid artery, cochlea, IAC, petrous ridge, and lateral border of V3. Conclusion The MF approaches are challenging. Operatively oriented skull base dissections provide a crucial foundation for learning these techniques. We describe comprehensive step-by-step approaches intended to develop familiarity in the cadaver laboratory and facilitate understanding of their potential for skull base disorders. Basic surgical principles are described to help in the operating room as well as illustrative cases.

Two-Stage Double Petrosal Approach for the Total Resection of Petroclival-Cavernous Meningioma: 2-Dimensional Operative Video

The utilization of skull base approaches has markedly facilitated the safe surgical removal of challenging petroclival meningiomas.1 The anterior petrosal approach has been utilized for tumors limited to the upper clivus, above the meatus, whereas the posterior petrosal approach has been the workhorse for the resection of larger tumors in the posterior fossa extending down the clivus.2 Giant cases with extension in the middle fossa, cavernous sinus, and ventral to the brain stem would benefit from a wider exposure than each of these approaches provide. This could be achieved by total petrosectomy. However, in patients with serviceable hearing anterior and posterior petrosals can be combined while preserving the hearing apparatus.2,3 This procedure is lengthy; hence, we tend to stage it in 2 subsequent days. The first stage is focused on the soft tissue and bone work including the mastoidectomy, sigmoid transverse sinus, and jugular bulb skeletonization, as well as anterior petrosectomy. The second stage is dedicated to tumor exposure through tentorial sectioning and microsurgical resection. We report the case of a 40-yr-old woman diagnosed with large left-sided petroclival meningioma with significant extension into the cavernous sinus and Meckel's cave. The patient had neurological deficits including cranial nerves, cerebellar dysfunction, and hydrocephalus, although her hearing was intact. Total tumor resection was achieved through the double petrosal approach in 2002. Extensive anatomic knowledge and thorough preoperative clinical and radiological evaluation, particularly the venous system, are key in the successful planning of this procedure. The patient consented for surgery and publication of their image. Figures at 2:40 and 3:47, ©Ossama Al-Mefty, used with permission.